Conventionally, there has been known a motor which includes a rotor including a plurality of sintered magnets arranged at a regular interval in a circumferential direction on an outer circumferential surface of a rotor core. For example, in a motor described in Patent Literature 1 mentioned below, a soft magnetic material (a high-magnetic permeability material) such as iron is used as a back yoke inside a rotor in order to decrease magnetic resistance in a magnetic circuit inside the motor (a stator core and the rotor).
Furthermore, in a rotor described in Patent Literature 2 mentioned below, a ring-shaped bond magnet obtained by kneading powder of a permanent magnet and resin is used as a magnetic pole. The powder of the permanent magnet has anisotropy, and by applying a magnetic field of polar anisotropy to the ring-shaped magnet from outside at the time of manufacturing, its magnetization direction has an orientation of polar anisotropy (hereinafter, “polar anisotropic orientation”). By causing the magnetization direction of the ring-shaped magnet have the polar anisotropic orientation in the above manner, a magnetic flux of a ring magnet is concentrated on the center of the magnetic pole, and hence high magnetization can be achieved even when a bond magnet having a low magnetic property is used. Further, with the polar anisotropic orientation, it is not necessary to provide a back yoke on a side of an inner circumference of the ring-shaped magnet. Therefore, both of reduction of a machining cost and weight reduction of the rotor can be realized at the same time. In addition, the ring-shaped magnet can be manufactured even with a sintered magnet, and because the sintered magnet has a density of magnet higher than that of the bond magnet, a magnetic force higher than that of the bond magnet can be obtained.